It is known to store solar energy, for subsequent use, concentrated by heliostats, fixed or tracking, within a receptor consisting of a block of material having a high thermal conductivity (typically graphite). Such block generally carries a suitably oriented cavity whereon said heliostats are directed. The receptor block, moreover, is typically associated to a heat exchanger having pipe bundles immersed in the same block and crossed by a working fluid—or carrier fluid, typically water, at the liquid or vapor state at a high temperature. The heat stored in the receptor block is transferred to such working fluid in order to produce vapor or heat for industrial plants.
In a system for storing solar energy in graphite block of the type described above, the temperatures involved may range from 400° C. to 2000° C. The upper temperature limit is bound by the thermal resistance of the heat exchanger, and in particular the metal pipe bundles thereof. In particular, in relation to the temperature difference between the incoming fluid and the exchanger pipes, the thermo-dynamic conditions of the fluid may change so quickly as to create strong stresses of the pipe metal (thermal and mechanical shocks), such as to subject the heat exchangers to extreme physical conditions, with the risk of excessive internal tensions and subsequent breakage.
Moreover, a difficulty of the systems described is to ensure continuity in the amount of heat removed by the accumulator, since the storage step is linked to the atmospheric conditions and to the day/night cycles. Known systems therefore are little versatile in terms of capability of adaptation to the downstream energy requirements.
In general, moreover, known systems are not optimized in terms of usage efficiency and conversion of the incoming electric energy.